Polysulfone hemodiafiltration membranes with enhanced anti-fouling and hemocompatibility modified by poly(vinyl pyrrolidone) via in situ cross-linked polymerization

Development and Investigation of a New Polysulfone Dialyzer with Increased Membrane Hydrophilicity

Innovation in dialysis care is fundamental to improve well-being and outcomes of patients with end-stage kidney disease. The dialyzer is the core element of dialysis treatments, as it largely defines which substances are removed from the patient's body. Moreover, its large surface size is the major place of interaction of the patient's blood with artificial surfaces and thus may lead to undesired effects such as inflammation or coagulation. In the present article we summarize the development path for a new dialyzer, including in vitro and clinical evidence generation. We use the example of the novel FX CorAL dialyzer, which has recently entered European and US markets, to show which steps are needed to develop and characterize a new dialyzer. The FX CorAL dialyzer includes a new hydrophilic membrane, which features reduced protein adsorption, sustained performance, and an improved hemocompatibility profile, characterized in numerous in vitro and clinical studies. Safety evaluations revealed a favorable profile, with low incidences of adverse device effects. Insights gained from both in vitro and clinical studies contribute to the advancement of dialyzer development, ultimately leading to improved patient care.

A Study on the Safety and Efficacy of an Innovative Hydrophilic Dialysis Membrane

The dialysis membrane based on a hydrophilic polymer (Hydrolink NV) was designed to enhance the movement of adsorbed water at the blood-membrane interface, aiming to achieve antithrombogenic and antifouling effects. This study aimed to assess the performance and albumin loss of the Hydrolink NV dialyzer in hemodialysis (HD) and post-dilution hemodiafiltration (HDF) with different infusion flows (Qis) and compare it with the hydrophilic FX CorAL dialyzer in post-dilution HDF. A prospective study was carried out in 20 patients. Patients underwent five dialysis sessions with the same routine dialysis parameters: four sessions with the Toraylight NV 2.1 (HD, post-dilution HDF with 50, 75 or auto-substitution Qi) and one with the FX CorAL 800 (post-dilution HDF with auto-substitution Qi). The reduction ratios' (RRs') wide range of molecular weight molecules were assessed and the dialysate albumin loss was quantified. The lowest β2-microglobulin, indoxyl-sulfate, and p-cresyl sulfate RR values were observed with the Toraylight NV 2.1 in HD, and they improved progressively with an increased Qi, without differences being observed between the two dialyzers in auto-substitution. A different removal profile was observed in terms of myoglobin, kFLC, prolactin, α1-microglobulin, α1-acid glycoprotein, and λFLC, whose RRs also improved progressively with an increased Qi but were significantly higher with the Toraylight NV than the CorAL in the same convective condition. There were significant differences in the albumin dialysate losses, with the highest value obtained with the Toraylight NV in auto-substitution HDF, with more than 50% of patients surpassing 5 g per session. The Toraylight NV dialyzer has great potential for efficacy but should be used at the optimal convective volume (Qi not exceeding 75 mL/min or FF not exceeding 25%) to avoid excessive albumin loss.

Preparation of an anticoagulant polyethersulfone membrane by immobilizing FXa inhibitors with a polydopamine coating

Anticoagulation treatment for patients with high bleeding risk during hemodialysis is challenging. Contact between the dialysis membrane and the blood leads to protein adsorption and activation of the coagulation cascade reaction. Activated coagulation Factor X (FXa) plays a central role in thrombogenesis, but anticoagulant modification of the dialysis membrane is rarely targeted at FXa. In this study, we constructed an anticoagulant membrane using the polydopamine coating method to graft FXa inhibitors (apixaban and rivaroxaban) on the membrane surface. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to characterize the membranes. The apixaban- and rivaroxaban-modified membranes showed lower water contact angles, decreased albumin protein adsorption, and suppressed platelet adhesion and activation compared to the unmodified PES membranes. Moreover, the modified membranes prolonged the blood clotting times in both the intrinsic and extrinsic coagulation pathways and inhibited FXa generation and complement activation, which suggested that the modified membrane enhanced biocompatibility and antithrombotic properties through the inhibition of FXa. Targeting FXa to design antithrombotic HD membranes or other blood contact materials might have great application potential.

Comparison of efficacy and safety of the new generation helixone dialyzers

INTRODUCTION

New generation helixone dialyzers has recently been developed as part of the ongoing effort to improve dialyzer hemocompatibility and avoid adverse reactions to synthetic dialyzers. This study aimed to assess the performance and albumin loss of this new dialyzer series in hemodiafiltration and compare it with the previous generation helixone series.

MATERIAL AND METHODS

A prospective study was conducted in 19 patients. Each patient underwent eight dialysis sessions with the same routine dialysis parameters; only the dialyzer varied: FX60 CorDiax, FX CorAL 60, FX600 CorDiax, FX CorAL 600, FX80 CorDiax, FX CorAL 80, FX800 CorDiax, and FX CorAL 800. The reduction ratios (RR) of urea, creatinine, ß2-microglobulin, myoglobin, kappa-free immunoglobulin light chains (κFLC), prolactin, α1-microglobulin, α1-acid glycoprotein, lambda immunoglobulin light chains (λFLC), and albumin were compared intra-individually. Dialysate albumin loss was also measured.

RESULTS

All treatments were well tolerated. The mean amount of replacement fluid ranged from 31 to 34 L. Comparison of dialysis treatments showed no differences between small molecules and even up to those the size of β2-microglobulins. Little differences were found between myoglobin, κFLC, prolactin, α1-microglobulin, and λFLC RRs, and only FX80 CorDiax was slightly superior to the others. Mean dialysate albumin losses were similar, with less than 2.5 g lost in each dialyzer. The FX80 CorDiax showed slightly higher global removal scores than the other dialyzers evaluated, except for FX CorAL 800.

CONCLUSION

The new generation helixone dialyzers series has been updated to minimise the risk of adverse reactions, while maintaining the effectiveness and albumin loss achieved by the previous most advanced helixone generation.

Hydrophilic Modification of Dialysis Membranes Sustains Middle Molecule Removal and Filtration Characteristics

While efficient removal of uremic toxins and accumulated water is pivotal for the well-being of dialysis patients, protein adsorption to the dialyzer membrane reduces the performance of a dialyzer. Hydrophilic membrane modification with polyvinylpyrrolidone (PVP) has been shown to reduce protein adsorption and to stabilize membrane permeability. In this study we compared middle molecule clearance and filtration performance of nine polysulfone-, polyethersulfone-, and cellulose-based dialyzers over time. Protein adsorption was simulated in recirculation experiments, while β2-microglobulin clearance as well as transmembrane pressure (TMP) and filtrate flow were determined over time. The results of this study showed that β2-microglobulin clearance (-7.2 mL/min/m2) and filtrate flow (-54.4 mL/min) decreased strongly during the first 30 min and slowly afterwards (-0.7 mL/min/m2 and -6.8 mL/min, respectively, for the next 30 min); the TMP increase (+37.2 mmHg and +8.6 mmHg, respectively) showed comparable kinetics. Across all tested dialyzers, the dialyzer with a hydrophilic modified membrane (FX CorAL) had the highest β2-microglobulin clearance after protein fouling and the most stable filtration characteristics. In conclusion, hydrophilic membrane modification with PVP stabilizes the removal capacity of middle molecules and filtration performance over time. Such dialyzers may have benefits during hemodiafiltration treatments which aim to achieve high exchange volumes.

Artificial intelligence application in adsorption of uremic toxins: Towards the eco-friendly design of highly efficient with potential applications as hemodialysis membranes

Six Functionalized Activated Carbon Cloths (FACCs) were designed to obtain fundamental information for training a Bayesian Regularized Artificial Neural Network (BRANN) capable of predicting adsorption capacity of the FACCs to synthesize tailor-made materials with potential application as dialysis membranes. Characterization studies showed that FACCs have a high surface area (1354-2073 m2 g-1) associated with increased microporosity (W0, average: 0.57 cm3 g-1). Materials are carbonaceous, with a carbon content between 69 and 92%. Chemical treatments modify the pHpzc of materials between 4.1 and 7.8 due to incorporating functional groups on the surface (C=O, -COOH, -OH, -NH, -NH2). Uremic toxins tests showed a high elimination rate of p-cresol (73 mg g-1) and creatinine (90 mg g-1) which is not affected by the matrix (aqueous solution and simulated serum). However, in the case of uric acid, adsorption capacity decreased from 143 mg g-1 to 71 mg g-1, respectively. When comparing the kinetic constants of the adsorption studies in simulated serum versus the studies in aqueous solution, it can be seen that this does not undergo significant changes (0.02 min-1), evidencing the versatility of the material to work in different matrices. The previous studies, in combination with characterization of the materials, allowed to establish the adsorption mechanism. Thus, it permitted to train the BRANN to obtain mathematical models capable to predict the kinetic adsorption of the toxins studied. It is concluded that the predominant adsorption mechanism is due to π-π interactions between the adsorbate unsaturations with the material's pseudo-graphitic planes. Results show that FACCs are promising materials for hemodialysis membranes. Finally, taking into consideration the adsorption capacities and rates, as well as the semiquantitative analysis of the environmental impact associated with the preparation of the adsorbents, the best adsorbent (CC, Eco-Scale = 91.5) was selected. The studies presented show that the material is eco-friendly and highly efficient in the elimination of uremic toxins.

Advances in Enhancing Hemocompatibility of Hemodialysis Hollow-Fiber Membranes

Hemodialysis, the most common modality of renal replacement therapy, is critically required to remove uremic toxins from the blood of patients with end-stage kidney disease. However, the chronic inflammation, oxidative stress as well as thrombosis induced by the long-term contact of hemoincompatible hollow-fiber membranes (HFMs) contribute to the increase in cardiovascular diseases and mortality in this patient population. This review first retrospectively analyzes the current clinical and laboratory research progress in improving the hemocompatibility of HFMs. Details on different HFMs currently in clinical use and their design are described. Subsequently, we elaborate on the adverse interactions between blood and HFMs, involving protein adsorption, platelet adhesion and activation, and the activation of immune and coagulation systems, and the focus is on how to improve the hemocompatibility of HFMs in these aspects. Finally, challenges and future perspectives for improving the hemocompatibility of HFMs are also discussed to promote the development and clinical application of new hemocompatible HFMs.

Graphical Abstract

Preparation and surface modification of ultrahigh throughput tannic acid coblended polyethersulfone ultrafiltration membranes for hemodialysis

Low dialysis and blood incompatibility efficiency are key issues to be addressed for polymeric hemodialysis membranes. To improve the comprehensive performance of hemodialysis membranes, polyethersulfone (PES)/tannic acid (TA) coblended ultrafiltration membranes were prepared and modified with a heparin‐like functionalized TA coating. The coblended TA improved the pore structure of the PES ultrafiltration membrane. And it could also undergo π‐π conjugation with the heparin‐like functionalized TA in the modified solution, resulting in a greater abundance of modified groups loaded on the membrane surface and pores close to the surface. The modified coating further improved the membrane performance. The physicochemical properties, solute filtration, and blood compatibility properties of the membrane were tested. The effect of TA on the pore structure of the membrane and the presence of modified layers were demonstrated by morphological and chemical structure analyses. The final modified membrane had an ultrahigh water flux (1053 L/m2·h), improved dialysis performance (BSA retention >99%, Lysozyme clearance >30% and Urea clearance >90%), and excellent hemocompatibility (The hemolysis rate was 1.31%, and APTT, PT, and TT values were increased by 40.8%, 74.2%, and 85.9%, respectively). This study shows that TA has great potential for improving the pore structure of polymeric membranes.

Hemodiafiltration: Technical and Medical Insights

Despite the significant medical and technical improvements in the field of dialytic renal replacement modalities, morbidity and mortality are excessively high among patients with end-stage kidney disease, and most interventional studies yielded disappointing results. Hemodiafiltration, a dialysis method that was implemented in clinics many years ago and that combines the two main principles of hemodialysis and hemofiltration-diffusion and convection-has had a positive impact on mortality rates, especially when delivered in a high-volume mode as a surrogate for a high convective dose. The achievement of high substitution volumes during dialysis treatments does not only depend on patient characteristics but also on the dialyzer (membrane) and the adequately equipped hemodiafiltration machine. The present review article summarizes the technical aspects of online hemodiafiltration and discusses present and ongoing clinical studies with regards to hard clinical and patient-reported outcomes.

Recent advancement challenges with synthesis of biocompatible hemodialysis membranes

The focus of this study is to enhance the protein fouling resistance, hydrophilicity, biocompatibility, hemocompatibility and ability of the membranes and to reduce health complications like chronic pulmonary disease, peripheral vascular disease, cerebrovascular disease, and cardiovascular disease after dialysis, which are the great challenges in HD applications. In the current study, the PSF-based dialysis membranes are studied broadly. Significant consideration has also been provided to membrane characteristics (e.g., flowrate coefficient, solute clearance characteristic) and also on commercially available polysulfone HD membranes. PSF has gained a significant share in the development of HD membranes, and continuous improvements are being made in the process to make high flux PSF-based dialysis membranes with enhanced biocompatibility and improved protein resistance ability as the major issue in the development of membranes for HD application is biocompatibility. There has been a great increase in the demand for novel biocompatible membranes that offer the best performances during HD therapy, for example, low oxidative stress and low change ability of blood pressure.

Impact of Membrane Modification and Surface Immobilization Techniques on the Hemocompatibility of Hemodialysis Membranes: A Critical Review

Despite significant research efforts, hemodialysis patients have poor survival rates and low quality of life. Ultrafiltration (UF) membranes are the core of hemodialysis treatment, acting as a barrier for metabolic waste removal and supplying vital nutrients. So, developing a durable and suitable membrane that may be employed for therapeutic purposes is crucial. Surface modificationis a useful solution to boostmembrane characteristics like roughness, charge neutrality, wettability, hemocompatibility, and functionality, which are important in dialysis efficiency. The modification techniques can be classified as follows: (i) physical modification techniques (thermal treatment, polishing and grinding, blending, and coating), (ii) chemical modification (chemical methods, ozone treatment, ultraviolet-induced grafting, plasma treatment, high energy radiation, and enzymatic treatment); and (iii) combination methods (physicochemical). Despite the fact that each strategy has its own set of benefits and drawbacks, all of these methods yielded noteworthy outcomes, even if quantifying the enhanced performance is difficult. A hemodialysis membrane with outstanding hydrophilicity and hemocompatibility can be achieved by employing the right surface modification and immobilization technique. Modified membranes pave the way for more advancement in hemodialysis membrane hemocompatibility. Therefore, this critical review focused on the impact of the modification method used on the hemocompatibility of dialysis membranes while covering some possible modifications and basic research beyond clinical applications.

Impact of Hydrophilic Modification of Synthetic Dialysis Membranes on Hemocompatibility and Performance

The dialyzer is the core element in the hemodialysis treatment of patients with end-stage kidney disease (ESKD). During hemodialysis treatment, the dialyzer replaces the function of the kidney by removing small and middle-molecular weight uremic toxins, while retaining essential proteins. Meanwhile, a dialyzer should have the best possible hemocompatibility profile as the perpetuated contact of blood with artificial surfaces triggers complement activation, coagulation and immune cell activation, and even low-level activation repeated chronically over years may lead to undesired effects. During hemodialysis, the adsorption of plasma proteins to the dialyzer membrane leads to a formation of a secondary membrane, which can compromise both the uremic toxin removal and hemocompatibility of the dialyzer. Hydrophilic modifications of novel dialysis membranes have been shown to reduce protein adsorption, leading to better hemocompatibility profile and performance stability during dialysis treatments. This review article focuses on the importance of performance and hemocompatibility of dialysis membranes for the treatment of dialysis patients and summarizes recent studies on the impact of protein adsorption and hydrophilic modifications of membranes on these two core elements of a dialyzer.

Immune System Dysfunction and Inflammation in Hemodialysis Patients: Two Sides of the Same Coin

Biocompatibility in hemodialysis (HD) has considerably improved in recent decades, but remains an open issue to be solved, appearing essential to reduce systemic inflammation and enhance patients’ clinical outcomes. Clotting prevention, reduction in complement and leukocyte activation, and improvement of antioxidant effect represent the main goals. This review aims to analyze the different pathways involved in HD patients, leading to immune system dysfunction and inflammation. In particular, we mostly review the evidence about thrombogenicity, which probably represents the most important characteristic of bio-incompatibility. Platelet activation is one of the first steps occurring in HD patients, determining several events causing chronic sub-clinical inflammation and immune dysfunction involvement. Moreover, oxidative stress processes, resulting from a loss of balance between pro-oxidant factors and antioxidant mechanisms, have been described, highlighting the link with inflammation. We updated both innate and acquired immune system dysfunctions and their close link with uremic toxins occurring in HD patients, with several consequences leading to increased mortality. The elucidation of the role of immune dysfunction and inflammation in HD patients would enhance not only the understanding of disease physiopathology, but also has the potential to provide new insights into the development of therapeutic strategies.

Fabrication, characterization, and performance of poly (aryl ether nitrile) flat sheet ultrafiltration membranes with polyvinyl pyrrolidone as additives

Poly(aryl ether nitrile) (PEN) was used to fabricate ultrafiltration membrane via immersion precipitation phase inversion method. The effects of polyvinyl pyrrolidone (PVP) of different molecular weights and concentrations on the structure and performance of PEN membranes were investigated. The membranes were observed by scanning electron microscope, atomic force microscope, equilibrium water content (EWC), porosity (ε), and so on. The membranes were subjected to ultrafiltration characterizations such as pure water flux (PWF), compaction factor (CF), hydraulic permeability (P m), and bovine serum albumin (BSA) rejection rate. The hydrophilicity was characterized by infrared spectroscopy and contact angle tests. Results showed that molecular weight of PVP had significant effect on PEN membrane formation, which the membrane prepared by PVP-k30 exhibited excellent comprehensive performance. Meanwhile, the concentration of PVP-k30 could effectively control the select-permeability of PEN membrane. With PVP-k30 concentration increased from 7 to 13 wt%, the prepared PEN membranes got higher EWC, ε, CF, and P m. The PWF increased from 146.5 to 249.1 L m−2 h−1 bar−1, while the overall rejection of BSA remained above 90%. Further increasing the addition amount to 16 wt%, the membrane performance began to decline. Finally, the addition of PVP-k30 could effectively improve the hydrophilicity of prepared PEN membrane surface.

Time-resolving characterization of molecular weight retention changes among three synthetic high-flux dialyzers

BACKGROUND

Toxin removal capacity (i.e. performance) of a dialyzer is not constant but diminishes during treatment, as the adsorption of proteins to the membrane provides an additional barrier to uremic solutes. We investigated time-resolving molecular weight retention changes among synthetic high-flux dialyzers and compare the results with recent data from a randomized controlled trial.

METHODS

In plasma recirculation experiments over 240min, sieving coefficients (SC) for β2-microglobulin, myoglobin and albumin were determined for the FX CorAL (Fresenius Medical Care), ELISIO (Nipro) and xevonta (B. Braun). Molecular weight retention (MWR) curves were generated and the shifts over 120min were characterized. Effective pore radius was determined, and the predicted albumin loss was compared with clinical data.

RESULTS

SC decreased over time for all dialyzers (mean relative decrease across all dialyzers: β2-microglobulin: 8.0% (120min); myoglobin: 56.6% (240min); albumin: 94.1% (240min)). FX CorAL (7.3%, 52.6% and 91.1%) and ELISIO (7.7%, 51.0% and 93.8%) showed a lower decrease than xevonta (9.0%, 66.2% and 97.4%). For all dialyzers, MWR curves shifted towards lower molecular weight, with the lowest shift for FX CorAL (by 0.23nm at SC50%, 120 min) and highest for xevonta (0.50nm). FX CorAL had the highest slope over time and the smallest decrease in the effective pore radius (2min: 2.31nm, 120min: 2.08nm). Predicted albumin loss over 4h was highest for xevonta (609.3mg) and comparable between ELISIO (283.6mg) and FX CorAL (313.3mg).

CONCLUSIONS

Substantial differences in the temporal performance profile of dialyzers exist. The present approach allows characterization of dialyzer permeability changes over time using standard, clinically relevant protein markers.

Anti-Biofouling Polymers with Special Surface Wettability for Biomedical Applications

The use of anti-biofouling polymers has widespread potential for counteracting marine, medical, and industrial biofouling. The anti-biofouling action is usually related to the degree of surface wettability. This review is focusing on anti-biofouling polymers with special surface wettability, and it will provide a new perspective to promote the development of anti-biofouling polymers for biomedical applications. Firstly, current anti-biofouling strategies are discussed followed by a comprehensive review of anti-biofouling polymers with specific types of surface wettability, including superhydrophilicity, hydrophilicity, and hydrophobicity. We then summarize the applications of anti-biofouling polymers with specific surface wettability in typical biomedical fields both in vivo and in vitro, such as cardiology, ophthalmology, and nephrology. Finally, the challenges and directions of the development of anti-biofouling polymers with special surface wettability are discussed. It is helpful for future researchers to choose suitable anti-biofouling polymers with special surface wettability for specific biomedical applications.

Polyvinylpyrrolidone in hemodialysis membranes: Impact on platelet loss during hemodialysis

INTRODUCTION

Hydrophilic modification with polyvinylpyrrolidone (PVP) increases the biocompatibility profile of synthetic dialysis membranes. However, PVP may be eluted into the patient's blood, which has been discussed as a possible cause for adverse reactions rarely occurring with synthetic membranes. We investigated the content of PVP and its elution from the blood-side surface from commercially available dialyzers, including the novel FX CorAL, with PVP-enriched and α-tocopherol-stabilized membrane, and link the results to the level of platelet loss during dialysis as a maker of biocompatibility.

METHODS

Six synthetic, PVP containing, dialyzers (FX CorAL, FX CorDiax [Fresenius Medical Care]; Polyflux, THERANOVA [Baxter]; ELISIO [Nipro]; xevonta [B. Braun]) were investigated in the present study. The content of PVP on blood-side surface was determined with X-ray photoelectron spectroscopy (XPS). The amount of elutable PVP was measured photometrically after 5 h recirculation. The level of platelet loss was evaluated in an ex vivo recirculation model with human blood.

FINDINGS

Highest PVP content on the blood-side surface was found for the polysulfone-based FX CorAL (26.3%), while the polyethersulfone-based THERANOVA (15.6%) had the lowest PVP content. Elution of PVP was highest for the autoclave steam-sterilized THERANOVA (9.1 mg/1.6 m² dialyzer) and Polyflux (9.0 mg/1.6 m² dialyzer), while the lowest PVP elution was found for the INLINE steam sterilized FX CorAL and FX CorDiax (<0.5 mg/1.6 m² dialyzer, for both). Highest platelet loss was found for xevonta (+164.4% compared to the reference) and the lowest for the FX CorAL (-225.2%) among the polysulfone-based dialyzers; among the polyethersulfone-based dialyzers, THERANOVA (+95.5%) had the highest and ELISIO (-52.1%) the lowest platelet loss.

DISCUSSION

Polyvinylpyrrolidone content and elution differ between commercially available dialyzers and were found to be linked to the membrane material and sterilization method. The amount of non-eluted PVP on the blood-side surface may be an important determinant for the biocompatibility of dialyzers.

Complement activation by dialysis membranes and its association with secondary membrane formation and surface charge

Activation of the complement system may occur during blood-membrane interactions in hemodialysis and contribute to chronic inflammation of patients with end-stage renal disease. Hydrophilic modification with polyvinylpyrrolidone (PVP) has been suggested to increase the biocompatibility profile of dialysis membranes. In the present study we compared the complement activation of synthetic and cellulose-based membranes, including the polysulfone membrane with α-tocopherol-stabilized PVP-enriched inner surface of the novel FX CorAL dialyzer, and linked the results to their physical characteristics. Eight synthetic and cellulose-based dialyzers (FX CorAL, FX CorDiax [Fresenius Medical Care]; Polyflux, THERANOVA [Baxter]; ELISIO, SUREFLUX [Nipro]; xevonta [B. Braun]; FDX [Nikkisio Medical]) were investigated in the present study. Complement activation (C3a, C5a, and sC5b-9) was evaluated in a 3 hours ex vivo recirculation model with human blood. Albumin sieving coefficients were determined over a 4 hours ex vivo recirculation model with human plasma as a surrogate of secondary membrane formation. Zeta potential was measured as an indicator for the surface charge of the membranes. The FX CorAL dialyzer induced the lowest activation of the three complement factors (C3a: -39.4%; C5a: -57.5%; and sC5b-9: -58.9% compared to the reference). Highest complement activation was found for the cellulose-based SUREFLUX (C3a: +154.0%) and the FDX (C5a: +335.0% and sC5b-9: +287.9%) dialyzers. Moreover, the FX CorAL dialyzer had the nearest-to-neutral zeta potential (-2.38 mV) and the lowest albumin sieving coefficient decrease over time. Albumin sieving coefficient decrease was associated with complement activation by the investigated dialyzers. Our present results indicate that the surface modification implemented in the FX CorAL dialyzer reduces the secondary membrane formation and improves the biocompatibility profile. Further clinical studies are needed to investigate whether these observations will result in a lower inflammatory burden of hemodialysis patients.

Resveratrol as a plant type antioxidant modifier for polysulfone membranes to improve hemodialysis-induced oxidative stress

Resveratrol (RES) is a plant extract with excellent antioxidant, biocompatibility, anti-inflammatory and inhibition of platelet aggregation. RES-modified polysulfone (PSF) hemodialysis membranes have been fabricated using an immersion phase transformation method. The antioxidant properties of the blend membranes were evaluated in terms of their 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS⁺), reactive oxygen species (ROS) free radicals scavenging, total antioxidant capacity (T-AOC) of serum and lipid peroxidation inhibition. The observed results of decreasing DPPH and ABTS⁺ levels, scavenging ROS, significant inhibition of lipid peroxidation and improving the T-AOC of serum all contribute to the recovery of oxidative balance and the use of RES as an antioxidant modifier. The antioxidant stability of PSF/RES blend membranes was also studied. Moreover, the results of blood compatibility experiments showed that the addition of RES improved the blood compatibility of PSF membrane, inhibited the adhesion of red blood cells and platelets; inhibited complement activation; and reduced the blood cells deformation rate. The dialysis simulation experiment indicated that PSF/RES membrane (M-3) can clear 90.33% urea, 89.50% creatinine, 74.60% lysozyme and retention 90.47% BSA. All these results showed the new PSF/RES blend membranes have potential to be used in the field of hemodialysis to improve oxidative stress status in patients.

A review on surface modification methods of poly(arylsulfone) membranes for biomedical applications

Considerable methods have so far been used for the surface modification of biomedical membranes. Several reviews and articles have been published on the improvements achieved in the field of poly(arylsulfone) membranes subjected to various surface modification methods and used in biomedical applications. This review concentrates on the surface modification, biological applications and future perspective of the poly(arylsulfone) biomedical membranes. Different surface modification procedures employed for the poly(arylsulfone) membranes have been classified, studied and compared. Diverse surface modification techniques include surface coating, chemical modification and immobilization/cross-linking, grafting, surface zwitterionicalization, mussel-inspired coating and layer-by-layer assembly. Furthermore, we review the recent research studies performed on the surface modification of the poly(arylsulfone) biomedical membranes. Meanwhile, the properties of biomedical membranes are also discussed in each section. At last, the future perspective and challenges of the strategies utilized for the surface modification of poly(arylsulfone) biomedical membranes are presented.

Hierarchical Surface Architecture of Hemodialysis Membranes for Eliminating Homocysteine Based on the Multifunctional Role of Pyridoxal 5'-phosphate

Patients with end-stage renal disease are prone to developing a complication of hyperhomocysteinemia, manifesting as an elevation of the homocysteine (Hcy) concentration in human plasma. However, Hcy as a protein-bound toxin is barely removed by conventional hemodialysis membranes. Here, we report a novel hemodialysis membrane by preparing a bioactive coating of pyridoxal 5'-phosphate (PLP) and adding biocompatible hyperbranched polyglycerol (HPG) brushes to achieve Hcy removal. The dip-applied PLP coating, a coenzyme with a role in Hcy metabolism, dramatically promoted a decrease in the Hcy concentration in human plasma. Moreover, the aldehyde group of PLP had an intrinsic chemical reactivity toward the terminal amino group to immobilize the HPG brushes on the hemodialysis membrane surface. The hierarchical PLP-HPG layer-functionalized membranes had a high efficacy for eliminating Hcy, with a concentration from the initial stage of 150 μmol/L reduced to a nearly normal level of 20 μmol/L in simulated dialysis. By analyzing the impact of HPG brushes with various chain lengths, we found that HPG brushes with a medium length enabled the PLP coating with the bioactive function of Hcy conversion to additionally protect Hcy-attacked target cells by providing excellent hydrophilicity and a dense enough chain volume overlap of the hyperbranched architecture. Simultaneously, the densely packed HPG brushes generated a maximal steric and hydration barrier that significantly improved biofouling resistance against blood proteins. The optimally functionalized membranes showed a clearance of 83.1% urea and 49.6% lysozyme and a rejection of 96.0% bovine serum albumin. The diversely functionalized PLP-HPG layers demonstrate a potential route for a more integrated hemodialysis membrane that can cope with the urgent issue of hyperhomocysteinemia in clinical hemodialysis therapy.

Highly Dual Antifouling and Antibacterial Ultrafiltration Membranes Modified with Silane Coupling Agent and Capsaicin-Mimic Moieties

Dual antifouling and antibacterial polysulfone(PSf)/polyethersulfone(PES) hybrid membranes were developed by the synergy of capsaicin-mimic N-(5-methyl acrylamide-2,3,4 hydroxy benzyl) acrylamide (AMTHBA) and vinyl triethylene (b-methoxy ethoxy) silane (VTMES). First, AMTHBA as a natural antimicrobial agent was incorporated into a casting solution via "microwave-assistance (MWA) in situ polymerization-blending" process to construct a hydroxyl-rich environment. Then, VTMES crosslinked to a hydroxyl-rich polymer matrix via hydrolytic condensation, and the influence of VTMES content on the hybrid membrane properties was systematically investigated. When the VTMES added amount was 1.0 wt %, the hybrid membrane achieved an optimal separation performance including a steady-state humic acid (HA) (5 mg/L) permeation flux of 326 L·m-2·h-1 and a rejection percentage of 97%. The antibacterial tests revealed that the hybrid membranes exhibited sustained bactericidal activity and effective inhibition of bacterial adhesion. Besides, the dual-functional membranes were clean as new after two-cycles filtration (with a cleaning efficiency of ~90%), indicating that the network silicone film on the surface benefits the foulant repellence. Hopefully, the dual-functional membranes constructed in this study can be applicable to the pretreatment stage of water treatment.

Recent advances in heparinization of polymeric membranes for enhanced continuous blood purification

Continuous blood purification technology such as hemodiafiltration has been used worldwide for saving patients suffering from severe diseases or organ function failure, especially in the intensive care unit and emergency setting. The filters as core devices are commonly made of polymer materials as hollow fiber membranes. However, the membrane is often inductively blocked by blood clot formation due to its interactions with blood components. Heparin is the anticoagulant often used in clinical practice for anti-coagulation. Recently, heparin is also employed to modify the hollow fiber membranes either chemically or physically to improve the filtration performance. This review summarizes recent advances in methodology for surface heparinization of such hollow fiber membranes, and their filtration performance improvement. The review also provides expert opinions for further research in this rapidly expanding field.

New perspectives on development of polysulfones/cellulose derivatives based ionic-exchange membranes: Dielectric response and hemocompatibility study

Due to the increasing need from the membrane technologies for diverse applications, development of new generation of materials with electroactive properties and significant impact on the future technological systems was imposed. An innovative way of designing the membrane materials with long-term stable hydrophilicity, enhanced workability, porosity, and good biocompatibility, has been adopted by blending of quaternized polysulfone (PSFQ) with a cellulose derivative (cellulose acetate phthalate, CAP). Moreover, the quaternization effect has significantly improved the electrical performances, in terms of the ionic conductivity, electron interactions, and dielectric properties, required by target applications, i.e., ionic-exchange membranes, IEMs. Results derived from dielectric spectroscopy confirm the enhanced dielectric quality, reflected by a low dielectric constant and dielectric loss at high frequency. Additionally, the relationship between the resulted dielectric properties and response at the blood-biomaterial interface, have confirmed their excellent performance, constituting the preliminary basis for future tests concerning their functionality as IEMs in hemodialysis.

Chronic wound healing: A specific antibiofilm protein-asymmetric release system

Chronic infection is a major cause of delayed wound-healing. It is recognized to be associated with infectious bacterial communities called biofilms. Currently used conventional antibiotics alone often reveal themselves ineffective, since they do not specifically target the wound biofilm. Here, we report a new conceptual tool aimed at overcoming this drawback: an antibiofilm drug delivery system targeting the bacterial biofilm as a whole, by inhibiting its formation and/or disrupting it once it is formed. The system consists of a micro/nanostructured poly(butylene-succinate-co-adipate) (PBSA)-based asymmetric membrane (AM) with controlled porosity. By the incorporation of hydrophilic porogen agents, polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG), we were able to obtain AMs with high levels of porosity, exhibiting interconnections between pores. The PBSA-PEG membrane presented a dense upper layer with pores small enough to block bacteria penetration. Upon using such porogen agents, under dry and wet conditions, membrane's integrity and mechanical properties were maintained. Using bovine serum albumin (BSA) as a model protein, we demonstrated that protein loading and release from PBSA membranes were affected by the membrane structure (porosity) and the presence of residual porogen. Furthermore, the release curve profile consisted of a fast initial slope followed by a second slow phase approaching a plateau within 24 h. This can be highly beneficial for the promotion of wound healing. Cross-sectional confocal laser scanning microscopy (CLSM) images revealed a heterogeneous distribution of fluorescein isothiocyanate (FITC) labeled BSA throughout the entire membrane. PBSA membranes were loaded with dispersin B (DB), a specific antibiofilm matrix enzyme. Studies using a Staphylococcus epidermidis model, indicate significant efficiency in both inhibiting or dispersing preformed biofilm (up to 80 % eradication). The asymmetric PBSA membrane prepared with the PVP porogen (PBSA-PVP) displayed highest antibiofilm activity. Moreover, in vitro cytotoxicity assays using HaCaT and reconstructed human epidermis (RHE) models revealed that unloaded and DB-loaded PBSA-PVP membranes had excellent biocompatibility suitable for wound dressing applications.

Toward Antibiofouling PVDF Membranes

Membranes for biologically and biomedically related applications must be bioinert, that is, resist biofouling by proteins, human cells, bacteria, algae, etc. Hydrophobic materials such as polysulfone, polypropylene, or poly(vinylidene fluoride) (PVDF) are often chosen as matrix materials but their hydrophobicity make them prone to biofouling, which in turn limits their application in biological/biomedical fields. Here, we designed PVDF-based membranes by precipitation from the vapor phase and zwitterionized them in situ to reduce their propensity to biofouling. To achieve this goal, we used a copolymer containing phosphorylcholine groups. An in-depth physicochemical characterization revealed not only the controlled presence of the copolymer in the membrane but also that bicontinuous membranes could be formed. Membrane hydrophilicity was greatly improved, resulting in the mitigation of a variety of biofoulants: the attachment of Stenotrophomonas maltophilia, Streptococcus mutans, and platelets was reduced by 99.9, 99.9, and 98.9%, respectively. Besides, despite incubation in a plasma platelet-poor medium, rich in plasma proteins, a flux recovery ratio of 75% could be measured while it was only 40% with a hydrophilic commercial membrane of similar structure and physical properties. Similarly, the zwitterionic membrane severely mitigated biofouling by microalgae during their harvesting. All in all, the material/process combination presented in this work leads to antibiofouling porous membranes with a large span of potential biomedically and biologically related applications.

Immobilization of Perylene-3,4,9,10-Tetracarboxylic Dianhydride on Hollow Polysulfone Fibers: Primary Amine Coupling and Fluorescence Reporting

The fluorescent dye perylene-3,4,9,10-tetracarboxylic dianhydride (PBA) was immobilized onto polysulfone hollow fibers by means of a wet coating procedure. After immobilization, PBA was able to react with primary amines through a double anhydride ring opening reaction. The in situ amine coupling was further revealed by fluorescence analysis. Both emission (534 nm →538 nm) and fluorescence lifetime changes (2.7 ns →3.3 ns) of the dye are a useful tool to detect and visualize the occurrence of the reaction. The successful implementation of amine coupling with a reporting function on polysulfone fibers holds great interest for biomedical applications.

Physical Processes in Polymeric Filters Used for Dialysis

The key physical processes in polymeric filters used for the blood purification include transport across the capillary wall and the interaction of blood cells with the polymer membrane surface. Theoretical modeling of membrane transport is an important tool which provides researchers with a quantification of the complex phenomena involved in dialysis. In the paper, we present a dense review of the most successful theoretical approaches to the description of transport across the polymeric membrane wall as well as the cell⁻polymer surface interaction, and refer to the corresponding experimental methods while studying these phenomena in dialyzing filters.

Preparation of Porous Polymeric Membranes Based on a Pyridine Containing Aromatic Polyether Sulfone

Polymeric membranes, based on a polysulfone-type aromatic polyether matrix, were successfully developed via the non-solvent induced phase separation (NIPS) method. The polyethersulfone type polymer poly[2-(4-(diphenylsulfonyl)-phenoxy)-6-(4-phenoxy) pyridine] (PDSPP) was used as the membrane matrix, and mixed with its sulfonated derivative (SPDSPP) and a polymeric porogen. The SPDPPP was added to impart hydrophilicity, while at the same time maintaining the interactions with the non-sulfonated aromatic polyether forming the membrane matrix. Different techniques were used for the membranes' properties characterization. The results revealed that the use of the non-sulfonated and sulfonated polymers of the same polymeric backbone, at certain compositions, can lead to membranes with controllable porosity and hydrophilicity.

Surface hemocompatible modification of polysulfone membrane via covalently grafting acrylic acid and sulfonated hydroxypropyl chitosan

In this study, acrylic acid (AA) and sulfonated hydroxypropyl chitosan (SHPCS) were covalently grafted on the PSf membrane surface to improve its hemocompatibility.